Polymer blends for use in making medical devices including catheters and balloons for dilatation catheters

ABSTRACT

A combination of polymeric components provides desired characteristics in forming medical instruments such as catheters and balloons for dilatation catheters. For example, a balloon material is formed from a blend of polymeric components, including a first crystalline polymeric component and a second softening polymeric component. Where the first two components are generally incompatible, the balloon material can also include a third compatibilizing agent to facilitate blending the first two polymeric components together. The first polymeric component can be a branched or straight chain polyamide having a molecular weight of at least about 5000, or a polyester prepared from aromatic dicarboxylic acids having 8 to 14 carbon atoms or aliphatic dicarboxylic acids having from 2 to 12 carbon atoms, and at least one glycol having the formula HO(CH 2 ) n  OH, where n is an integer from 2 to 10, neopentyl glycol and cyclohexane dimethanol. The second polymeric component can be a polyolefin, an ethylene copolymer, a polyester block copolymer, or a polyamide block copolymer. The third polymeric component is preferably an ethylene copolymer having the formula E/X/Y where E is ethylene; X is an α, β-ethylenically unsaturated monomer derived from at least one of alkylacrylate, alkylmethacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, or mixtures thereof, where the alkyl groups contain 1-12 carbon atoms; and Y is an α, β-ethylenically unsaturated monomer containing a reactive group that forms a covalent bond with the first polymeric component. The polymeric blend can be irradiated to enhance the properties of the balloon material, including significantly increasing burst pressures.

This application is a continuation, of application Ser. No. 08/481,875filed Jun. 7, 1995 now abandoned, which is a Divisional of Ser. No.08/280,764, filed Jul. 25, 1994, now U.S. Pat. No. 5,554,120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a novel polymer blend that can beextruded, molded, or otherwise formed into articles of manufacturehaving certain desired characteristics. As examples, the polymer blendof the invention can be processed to form medical catheters and moreparticularly concerns a balloon material for medical balloon dilatationcatheters made from blends of a first crystalline polymer component, anda second softening polymer component. The balloon material can alsoinclude a third compatibilizing polymer component. While the inventionherein relates generally to polymer blends, it will be discussed interms of preferred end uses in medical devices such as catheters anddilatation balloons. The subsequent discussion is not meant to belimiting and is by way of examples and preferred uses.

2. Description of Related Art

Catheters are well known for their usefulness in medical applicationsand in particular angioplasty procedures, for opening blood vessels orother passageways in the body that may be blocked by obstructions orstenosis. Dilatation catheters are generally formed from thin, flexibletubing having an inflatable balloon at or near a distal tip of thetubing that can be inflated with fluid pressure communicated to theballoon through a lumen of the tubing. In a typical angioplastyprocedure, the balloon dilatation catheter is passed through thevasculature to the location of a stenosis in an artery, and the balloonis inflated to a predetermined size and shape to open the blockedartery.

It is desirable for balloons of balloon dilatation catheters to becapable of inflating to a diameter of typically five to six times theiruninflated diameter in order to be able to open an obstructed vessel.Other desirable properties of balloons for such balloon dilatationcatheters include strength, softness, flexibility and a thin, lowprofile which are important for achieving the performancecharacteristics of folding in an uninflated state, tracking, crossingand recrossing the area of the obstruction or stenosis in a vessel in anuninflated state. In addition, properties of burst strength, compliance,fatigue have been increasingly important in the continuing effort tocreate thinner, lower profile balloons for balloon dilatation catheterswith an ability to track, cross and recross increasingly narrow passagesin obstructed vessels. For purposes of this description, the ability tocross is defined as the ability of a balloon of a balloon dilatationcatheter to pass through a stenosis; the ability to recross is definedas the ability of the balloon of a balloon dilatation catheter to passthrough a stenosis more than once, or to pass through more than onestenosis; and the ability to track is defined as the ability of balloonof a balloon dilatation catheter to pass over a guidewire through thetortuous curves of the vasculature, in being guided to and from thelocation of a stenosis.

Polymeric materials that have been used for making medical devices,catheters, dilatation catheters, and balloons for balloon dilatationcatheters include polyethylene, polyolefins, polyvinyl chloride,polyester, polyimide, polyethylene terephthalate (PET), polyamides,nylon, polyurethane, and the like. Balloons made of soft polyolefin orethylene copolymers materials are typically foldable, and track andcross well, so that they can often be used more than once, and can beused to cross multiple lesions. However, such balloons also commonlyhave high balloon compliance and low burst strengths, with ratings ofrated burst pressure of about 8-9 atm, and a mean burst pressure ofabout 10-15 atm. Balloons made from polyethylene terephthalate (PET) arecommonly stronger, with a higher rated burst pressure of about 14-18atm, and a mean burst pressure of about 18-25 atm. However, dilatationcatheter balloons made of PET are generally stiff, not readily foldableand refoldable, and are susceptible to acquiring defects from mechanicalhandling. Dilatation catheter balloons made of PET are also susceptibleto pin-hole failures that can cause jet-streaming of pressurized fluidwithin an artery, and can lead to a dissection of the artery. As aresult, to reduce the likelihood of pin-hole failures, clinicalapplications of balloons made of this type of material have generallybeen limited to thicker balloons that are commonly limited to a singleuse, and for crossing a single lesion.

Examples of prior art compositions that may be suitable in formingmedical devices such as catheters, dilatation catheters, and balloonmaterials for use in angioplasty procedures include U.S. Pat. No.4,753,980 (Deyrup) ; U.S. Pat. No. 4,172,859 (Epstein) ; U.S. Pat. No.5,091,478 (Saltman) ; U.S. Pat. No. 5,306,246 (Sahatjian et al.); U.S.Pat. No. 4,254,774 (Boretos); U.S. Pat. No. 4,964,409 (Tremulis); andU.S. Pat. No. 5,017,325 (Jackowski et al.), all of which areincorporated herein by reference. These references are presented by wayof example only and are not intended to be exhaustive of the prior art.

It would be desirable to provide a polymeric blend for balloons forballoon dilatation catheters with a combination of the best features ofthe softer balloon materials and the stronger balloon materials,including good flexibility, folding, track, cross and recross, with athin, low profile, high resistance to fatigue, low compliance, and highburst strength, with a lower susceptibility to defects throughmechanical handling, and a lower susceptibility to pin-hole defects,compared with balloons made from PET. The present invention meets theseneeds.

SUMMARY OF THE INVENTION

Briefly, and in general terms, the present invention provides for acatheter and/or balloon material formed from a blend of polymericcomponents that has surprisingly high rated and mean burst pressurecharacteristics, low compliance and excellent fatigue resistance, alongwith excellent folding and performance characteristics, such as track,cross and recross, allowing for construction of dilatation catheterballoons with the ability to cross multiple lesions.

The invention accordingly provides for a catheter and/or balloonmaterial formed from a blend composition of a first crystallinepolymeric component and a second softening polymeric component. When thefirst and second polymeric components are essentially incompatible inthat they are immiscible, and do not normally bond together well, athird compatibilizing agent that helps to strengthen the interfacebetween the two incompatible materials and to facilitate blending of thefirst two polymeric components can be added to the balloon material.

The first polymeric component generally consists of about 10-95% byweight of the total blend composition, and in one preferred embodimentcan be a polyester prepared from the group of dicarboxylic acidsselected from aromatic dicarboxylic acids having from 8 to 14 carbonatoms and aliphatic dicarboxylic acids having from 2 to 12 carbon atoms,and at least one glycol selected from the group consisting of glycolshaving the formula HO(CH₂)_(n) OH, where n is an integer from 2 to 10,neopentyl glycol and cyclohexane dimethanol. In an alternativeembodiment, the first polymeric component can be a branched or straightchain polyamide having a molecular weight of at least about 5000. Thesecond polymeric component generally consists of about 5-90% by weightof the total blend composition, is selected to have a Shore hardnessless than 75 D, and preferably less than 55 D, and is selected from thegroup consisting of ethylene copolymers, polyolefins having a densityless than 0.93, polyester block copolymers and polyamide blockcopolymers. The third polymeric component generally consists of anamount of a compatibilizing ethylene copolymer that is less than about2.5% by weight of the total balloon material blend, and preferably about0.25% to about 2.5% by weight of the total balloon material blend, andhas the formula E/X/Y where E is ethylene; X is an α, β-ethylenicallyunsaturated monomer derived from at least one of vinyl acetate,alkylacrylate, alkylmethacrylate, alkyl vinyl ether, carbon dioxide,sulfur dioxide, or mixtures thereof, where the alkyl groups contain 1-12carbon atoms; and Y is an α, β-ethylenically unsaturated monomercontaining a reactive group that will form a covalent bond with thefirst polymeric component. Alternatively, suitable catheter and/orballoon materials can be prepared that contain up to about 20% by weightof the third polymeric component.

The first polymeric component preferably comprises about 60-77% of thetotal blend composition, and in a preferred embodiment is selected fromthe group consisting of polyethylene-terephthalate,polybutylene-terephthalate, glycol modified polyethylene-terephthalate,1,4-cyclohexylene dimethylene terephthalate/isophthalate copolymer,linear homopolymer esters derived from aromatic dicarboxylic acids andglycols of the general formula HO(CH₂)_(n) OH where n is an integer from2 to 10. In a preferred aspect of the invention, the second polymericcomponent is a softening ethylene copolymer comprising about 23-40% byweight of the total blend composition, and contains ethylene and atleast one other monomer selected from the group consisting of α,β-ethylenically unsaturated monomers, carbon monoxide, and sulfurdioxide. In one particularly preferred embodiment, the softeningethylene copolymer has the formula E'X' or E'X'Y', where E' is ethylene,and is about 60-85% by weight of the ethylene copolymer, and where X' isabout 15-40% by weight of the ethylene copolymer, and X' is selectedfrom the group consisting of methylacrylate, ethylacrylate,propylacrylate, butylacrylate, and mixtures thereof, and Y', if present,is an α, β-ethylenically unsaturated monocarboxylic acid, di-acid oranhydride comprising about 0.5-15% by weight of the ethylene copolymer.Examples of Y' include but are not limited to acrylic acid, methacrylicacid, fumaric acid and maleic anhydride. Where one of the X' or Y'monomers is an acid containing moiety, the polymer can also be at leastpartially neutralized with an ion selected from the group of sodium,potassium, zinc, lithium, calcium, and ammonium. In a preferredembodiment, in the third polymeric component, X is selected from thegroup consisting of vinyl acetate, methylacrylate, butylacrylate, andmethyl vinyl ether, Y is an α, β-ethylenically unsaturated monomercontaining a reactive group selected from the group consisting ofepoxide, maleic anhydride, isocyanate, or oxazoline. In one preferredembodiment, Y is selected from the group consisting of glycidylacrylate, glycidyl methacrylate, and epoxide containing copolymerizablemonomers. In one currently particularly preferred embodiment, in thethird polymeric component, E is ethylene, and is 67% by weight of thecompatibilizing ethylene copolymer; X is selected from the group ofmethylacrylate, ethylacrylate, and butylacrylate, and is about 15-30% byweight of the compatibilizing agent; and Y is selected from the groupconsisting of glycidyl acrylate and glycidyl methacrylate, and is about8% by weight of the compatibilizing agent.

These and other aspects and advantages of the invention will becomeapparent from the following detailed description of the preferredembodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a polymer blend having certaincharacteristics generally desirable in medical devices. The polymerblend described herein is particularly suitable for use in formingmedical products such as catheters, dilatation catheters, and preferablyballoon material for use with catheters.

While dilatation catheter balloons made of soft polyolefin or ethylenecopolymer materials have generally good performance characteristics,such balloons also commonly have high balloon compliance and low burststrengths. Dilatation catheter balloons made from strong polymericmaterials such as polyethylene terephthalate (PET) have higher rated andmean burst pressures, but are generally stiff, not readily foldable andrefoldable, and are susceptible to acquiring defects from mechanicalhandling, and are susceptible to pin-hole failures that can seriouslyinjure the vasculature of a patient. While the embodiments discussedherein refer generally to balloon materials, it is to be understood thatthe invention relates to catheters as well having the polymer blends asdescribed.

The invention accordingly is embodied in a balloon material for balloondilatation catheters with a combination of the best features of thesofter balloon materials and the stronger balloon materials, includinghigh burst strength, low compliance, good flexibility, high resistanceto fatigue, the ability to fold, track, cross and recross well, and witha lower susceptibility to defects through mechanical handling, and alower susceptibility to pin-hole defects, compared with balloons madefrom PET. The balloon material is formed from a blend of three polymericcomponents, comprising a strong polymeric component, a softeningpolymeric component that are generally incompatible, and acompatibilizing polymeric component that forms a covalent bond with oneof the first two polymeric components, and prevents the first twopolymeric components from separating when formed as a balloon for aballoon dilatation catheter.

The first polymeric component, component A, is preferably a relativelystrong crystalline polymer, preferably comprising about 60-77% of thetotal blend composition, although blend compositions of the inventioncomprising as little as 10% or as much as 95% of the total blendcomposition may also be suitable. In one currently preferred embodiment,component A comprises PET, but can also comprise other polyesters, orpolyamides. Other polyesters which can be used as component A includepolyesters prepared from an aromatic dicarboxylic acid having from 8 to14 carbon atoms and at least one glycol, including those having theformula HO(CH₂)_(n) OH where n is an integer of 2 to 10, neopentylglycol and cyclohexane dimethanol. The dicarboxylic acid may also be analiphatic dicarboxylic acid having from 2 to 12 carbon atoms. Examplesof other suitable polyesters include, but are not limited to,polybutylene-terephthalate (PBT), glycol modified PET (PETG),1,4-cyclohexylene dimethylene terephthalate/isophthalate copolymer andother linear homopolymer esters derived from aromatic dicarboxylic acidsand glycols of the general formula HO(CH₂)_(n) OH where n is an integerfrom 2 to 10. Such aromatic dicarboxylic acids include isophthalic,bibenzoic, naphthalene-dicarboxylic including the 1,5-; 2,6-; and2,7-naphthalenedicarboxylic acids; 4,4'-diphenylenedicarboxylic acid;bis(p-carboxyphenyl) methane; ethylene-bis-p-benzoic acid;1,4-tetramethylene bis(p-oxybenzoic) acid; ethylene bis(p-oxybenzoic)acid; 1,3-trimethylene bis(p-oxybenzoic) acid; and 1,4-tetramethylenebis(p-oxybenzoic) acid.

Preferred glycols include ethylene glycol; 1,3-trimethylene glycol;1,4-tetramethylene glycol; 1,6-hexamethylene glycol; 1,8-octamethyleneglycol; 1,10-decamethylene glycol; 2,2-dimethyl-1,3-propane diol;1,3-propylene glycol; 1,4-butylene glycol; neopentyl glycol andcyclohexane dimethanol.

Polyamides which are suitable for use as component A include branched orstraight chain polyamides having a molecular weight of at least 5000,and commonly referred to as nylons; produced by condensation ofequimolar amounts of a saturated dicarboxylic acid containing from 4 to12 carbon atoms with a diamine, in which the diamine contains from 4 to12 carbon atoms. Examples of suitable polyamides include, but are notlimited to, nylons such as polyhexamethylene adipamide (nylon 6,6),polyhexamethylene azelaamide (nylon 6,9), polyhexamethylene sebacamide(nylon 6,10), polyhexamethylene dodecanoamide (nylon 6,12), nylon 6,nylon 11, and nylon 12. Other polyamides that can be suitable includepolyamide block copolymers such as those sold under the trade name"PEBAX" by Atochem; polyamides including polyamides produced by the ringopening of lactams such as polycaprolactam, polylauric lactam,poly-11-amino-undecanoic acid, and bis(paraaminocyclohexyl) methanedodecanoamide; and polyamides prepared by the copolymerization orterpolymerization of such polymers. The polyamides preferably have amelting point in excess of 200° C.

The second polymeric component, component B, is selected to be asoftening polymer, preferably comprising about 23-40% by weight of thetotal balloon material composition, although blends of the balloonmaterial comprising as little as 5% of component B and as much as 90% ofthe total blend composition may also be suitable. In a currentlypreferred embodiment, component B comprises a softening polymercomponent having a Shore hardness less than 75 D, and preferably lessthan 55 D, and is preferably an elastomeric ethylene copolymer selectedfrom the group of ethylene copolymers comprising ethylene and at leastone other monomer selected from the group of α, β-ethylenicallyunsaturated monomers, carbon monoxide (CO), sulfur dioxide (SO₂).Component B is most preferably an elastomeric ethylene copolymer havingthe formula E'X' or E'X'Y', where E' is ethylene and comprises about60-85% by weight of the ethylene copolymer, X' is acrylate ormethacrylate monomer, comprising about 15-40% of the ethylene copolymer,and Y', if present, is an α, β-ethylenically unsaturated monocarboxylicacid, di-acid or anhydride comprising about 0.5-15% by weight of theethylene copolymer. Examples of Y' include but are not limited toacrylic acid, methacrylic acid, fumaric acid and maleic anhydride. Otherpolymeric materials that may be suitable for use as component B include,but are not limited to, polyester block copolymers (containing one ormore of the following glycols) comprising hard segments ofpolyethylene-terephthalate or polybutylene-terephthalate, and softsegments of polyether such as polyethylene glycol, polypropylene glycolor polytetramethylene glycol ethers, such as those available under thetradename "HYTREL" from DuPont. Long chain glycols which can be used toprepare such copolyester polymers include poly(alkylene oxide) glycolsin which the alkylene group has 2-10 carbon atoms, such as poly(ethyleneoxide) glycol, poly(1,2- and 1,3-propylene oxide) glycol,poly(tetramethylene oxide) glycol, poly(pentamethylene oxide) glycol,poly(hexamethylene oxide) glycol, poly(heptamethylene oxide) glycol,poly(octamethylene oxide) glycol, poly(nonamethylene oxide) glycol, andpoly(1,2-butylene oxide) glycol, random or block copolymers of ethyleneoxide and 1,2-propylene oxide, and poly-formals prepared by reactingformaldehyde with glycols, such as propylene glycol, or mixtures ofglycols, such as a mixture of tetramethylene and pentamethylene glycols,and glycols formed from dicarboxymethyl acids of poly(alkylene oxides);polyetherimide esters such as those produced under the tradename "LOMOD"by General Electric; polyesters available from Dutch State Mines underthe trade name "ARNITEL"; polyamide block copolymers, such as thoseavailable from Atochem under the tradename "PEBAX"; and polyolefinshaving a density less than 0.93, including elastomericethylene-propylene copolymers, linear low density polyethylene (LLDPE),and linear low density polyethylene (LLDPE) including maleic anhydride.

The most preferred ethylene copolymers which can be used as component Binclude, but are not limited to, ethylene/methylacrylate/sulfur dioxide(E/MA/SO₂), ethylene/butylacrylate/carbon monoxide (E/BA/CO),ethylene/methylacrylate (E/MA), ethylene ethylacrylate (E/EA),ethylene/butylacrylate (E/BA), ethylene/vinylacetate (E/VA),ethylene/methacrylic acid (E/MAA or E/AA),ethylene/butylacrylate/methacrylic acid (E/BA/MAA or E/BA/AA),ethylene/methylacrylate/methacrylic acid (E/MA/MAA or E/MA/AA),ethylene/butylacrylate/maleic anhydride (E/BA/Manh) orethylene/methylacrylate/maleic anhydride (E/MA/Manh). Where one of theα, β-ethylenically unsaturated monomers is an acid containing moiety,the polymer can be partially neutralized with an ion such as Na+, K+,Zn++, Li+, Ca++, NH4+, or the like. The acid groups in the unsaturatedmono-carboxylic acid are neutralized from 0-80% by at least one metalion selected from the group consisting of sodium, zinc, magnesium,calcium, potassium, and lithium. The third polymeric component,component C, is preferably an ethylene copolymer that functions as acompatibilizing agent or surfactant, in that it forms a covalent bondwith the first polymeric component, and blends compatibly with thesecond polymeric component. Component C preferably comprises from zeroto about 2.5% of the total blend composition, having the formula E/X/Y,where E is about 67%, X is about 25%, and Y is about 8% by weight of thecompatibilizing ethylene copolymer, and

E is ethylene,

X is an α, β-ethylenically unsaturated monomer derived from at least oneof alkylacrylate, alkylmethacrylate, alkyl vinyl ether, carbon dioxide,sulfur dioxide, or mixtures thereof, where the alkyl groups contain 1-12carbon atoms, such as vinyl acetate, methylacrylate, butylacrylate, andmethyl vinyl ether. X can, for example be a moiety derived from at leastone of alkyl acrylate, alkyl methacrylate, alkyl vinyl ether, carbonmonoxide, sulfur dioxide, or mixtures thereof. More specifically, X can,for example, consist of 0-35 weight percent of a moiety derived from atleast one alkyl acrylate, alkyl methacrylate, or mixtures thereof wherethe alkyl groups contain 1-8 carbon atoms.

Y is an α, β-ethylenically unsaturated monomer containing a reactivegroup, such as epoxide, maleic anhydride, isocyanate, or oxazoline, forexample, that forms a covalent bond with said first polymeric component.In one preferred embodiment, Y is selected from the group consisting ofglycidyl methacrylate and glycidyl acrylate, maleic anhydride, andisocyanato-ethylmethacrylate.

In one currently preferred embodiment the first polymeric component ofthe balloon material blend comprises about 70-77% by weight PET; about23-30% by weight of component B, which comprises an ethylene copolymerhaving the formula E'X', where E' is ethylene, and is about 75% byweight of the ethylene copolymer, and X' is selected from the group ofethylene methylacrylate, ethylene ethylacrylate, ethylenepropylacrylate, and ethylene butylacrylate, and is about 25% by weightof the ethylene copolymer; and from about 0.25% to about 2.5% by weightof component C, which is an ethylene copolymer having the formula EXY,where E is ethylene, and is 67% by weight of component C; X is selectedfrom the group of ethylene acrylate and ethylene methylacrylate, and isabout 25% by weight of component C; and Y is selected from the groupconsisting of glycidyl methacrylate, glycidyl ethylacrylate, andglycidyl butylacrylate, and is about 8% by weight of component C. Thesecond polymeric component, component B, is most preferably anelastomeric ethylene copolymer selected from the group consisting ofethylene/methylacrylate, ethylene/ethylacrylate, ethylene/butylacrylate,ethylene/methylacrylate/maleic anhydride, ethylene/ethylacrylate/maleicanhydride, and ethylene/butylacrylate/maleic anhydride; and the thirdpolymeric component, component C, is most preferably an ethyleneacrylate ester where X is selected from methyl acrylate, ethyl acrylateand butyl acrylate, and Y is selected from the group consisting ofglycidyl acrylate and glycidyl methacrylate.

In addition, in a preferred aspect of the invention, the balloonmaterial of the invention can advantageously be irradiated usingionizing radiation from an electron beam, gamma rays, ultraviolet light,or a molecular beam, to significantly alter the properties of theballoon material to provide improved balloon performance such as higherburst pressures. For example, where the balloon material was subjectedto an electron beam of about 10-100 MRads and energies of 100-200,000keV, higher burst strengths and higher fatigue strengths were obtainedfrom the balloon material.

The balloon materials of the invention provide dilatation catheterballoons with the ability to cross multiple lesions, good track, cross,and folding, low compliance with rated burst pressures of about 10-15atm, and mean burst pressures of about 14-20 atm. Balloons made from theballoon material of the invention also typically have a lowersusceptibility to defects through mechanical handling than PET. Whenexposed to ionizing radiation to toughen the balloon material, thefatigue and burst strengths are substantially increased, to give ratedburst pressures of 12-14 atm or greater, mean burst pressures of 19-20atm, and a compliance of about 0.02-0.03 (mm/atm).

EXAMPLE 1

A polymer blend containing 80 weight % PET Traytuf 9506C manufactured byShell, and 20 weight % ethylene ethylacrylate (EEA) DPDA 6182manufactured by Union Carbide, was produced by compounding in a twinscrew extruder set for low shear conditions. The PET and EEA were mixedin a weight ratio of 80/20. The PET/EEA mixture was loaded into thehopper of the compounder. The barrel temperatures were set to 410° F. inzone 1, 490° F. in zones 2 and 3, and 480° in zone four and at the headof the barrel, the screw speed was maintained at 150 RPM, and thematerial was pelletized. Balloon tubing having an inner diameter of0.018 inches and an outer diameter of 0.036 inches was extruded usingthe 80/20 PET/EEA blend. The 80/20 PET/EEA blended material was dried.The barrel and die temperatures of the extruder were set, with zone 1 at390° F., zone 2 at 480° F., zone 3 at 500° F., and the clamp, die 1 anddie 2 at 510° F. The melt temperature of the blend was 574° F.Examination with a scanning electron microscope of a portion of theblend before extrusion into balloon tubing showed that the EEA formedspherical particles with a diameter greater than one micron, with poorinterfacial adhesion within the PET matrix. A section of the extrudedballoon tubing was also examined with a scanning electron microscope,showing that the EEA formed tubules in the extruded balloon tubing thatpulled out of the PET matrix.

EXAMPLE 2

The blend of PET and EEA from Example 1 was compounded and blended with2% of the total blend composition by weight of a third component,E/EA/GMA, as a compatibilizer, available as Lotader AX8660 from AtoChem.Examination with a scanning electron microscope of a portion of theblend before extrusion into balloon tubing showed that the EEA formed amuch better dispersion with better interfacial adhesion within the PETmatrix, with little or no particle pull-out from the PET matrix. Asection of the extruded balloon tubing made from the blend was alsoexamined with a scanning electron microscope, showing that the EEAformed no tubules in the extruded balloon tubing, and that the dispersedparticles of EEA were well adhered to the PET matrix. The material had aburst pressure of about 50 psi higher than in Example 1.

EXAMPLES 3-10

Balloon material blends were also formed using PET available as Traytuf9506C from Shell, with a tensile strength of 7000 psi (non-oriented),and 10000-12000 (oriented), an elongation of 400-500% (after yield), aflexural modulus of 500,000-600,000 psi, and a melting point of 257° C.EEA available as DPDA 6182 from Union Carbide was used in Examples 3-5and 8-10, with a tensile strength of 2300 psi, elongation of 670%, aflexural modulus of 6400 psi, a melt index of 1.5, a durometer of 91 A,a melting point of 85 C, a density of 0.93 and a Vicat Softening indexof 64. EMAC available as TC130 from Exxon was used in Examples 6 and 7,with a tensile strength of 1200 psi, an elongation of 1600%, a flexuralmodulus of 3300 psi, a melt index of 20, a Durometer of 85 A, a meltingpoint of 79 C., a density of 0.94 and a Vicat Softening index of 50.Lotryl 24MA005 (EMA) from AtoChem was used as the softening component inExample 10, with a tensile strength of 2910 psi, elongation of 700%,a-melt index of 0.5, a Durometer of 84 A, a melting point of 70 C., anda Vicat Softening index of 43. Lotader AX8660 (67% E, 25% EA, 8% GMA)from Atochem was used as the compatibilizing agent in Examples 4-10,with a tensile strength of 509 psi, an elongation of 700%, a melt indexof 6.0, a Durometer of 60 A, a melting point of 63 C., and a VicatSoftening index of 34.

The blend compositions of Examples 3-10 are listed in Table I below, andwere compounded under the compounding conditions noted in Table II andwere extruded under the tubing extrusion conditions noted in Table III.

                  TABLE I                                                         ______________________________________                                        Example                                                                              PET %    EEA %   EMAC %  Lotryl %                                                                             Lotader %                              ______________________________________                                        3      60       40      --      --     --                                       4 78.4 19.6 -- -- 2                                                           5 76   19   -- -- 5                                                           6 78.4 --   19.6 -- 2                                                         7 76   -- 19 -- 5                                                             8 68.8 29.5 -- --   1.7                                                       9 59.1 39.4 -- --   1.5                                                       10  70   -- -- 28 2                                                         ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Example 3      4      5    6    7    8    9    10                             ______________________________________                                        T1 ° F.                                                                        410    410    410  400  400  400  400  275                              T2 ° F. 490 480 480 480 480 450 450 480                                T3 ° F. 490 480 480 490 490 485 485 535                                T4 ° F. 480 500 500 515 515 500 500 555                                Thead ° F. 480 500 500 515 515 500 500 555                             RPM 150 150 150 150 150 150 150 150                                           Dry ° F. 300 200 200 200 200 200 200 200                             ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Example  3      4        5    6      8    10                                  ______________________________________                                        T1 ° F.                                                                         390    400      400  370    400  405                                   T2 ° F. 480 480 480 430 480 485                                        T3 ° F. 500 510 510 480 500 490                                        Tclamp 510 510 510 480 500 490                                                ° F.                                                                   Tdie1 510 510 510 480 500 490                                                 ° F.                                                                   Tdie2 510 510 510 480 500 500                                                 ° F.                                                                   I.D. .018  .020  .020  .020  .020  .020                                       inches                                                                        O.D. .036  .040  .040  .040  .040  .040                                       inches                                                                        Dry ° F. 150 150 150 150 150 150                                     ______________________________________                                    

EXAMPLE 11

In Example 11, a blend composition was compounded according to themethod of Example 1. Tubing was extruded with an inner diameter of 0.18inches, an outer diameter of 0.036 inches, and a double wall thickness(DWT) of 0.00135 inches. The balloon formed from the tubing wassubjected to 25 Mrads of radiation, and had a mean burst pressure of 250psi.

EXAMPLES 12-13

In Examples 12 and 13, a blend composition was compounded according tothe method of Example 2. In Example 12, tubing was extruded with aninner diameter of 0.020 inches and an outer diameter of 0.040 inches.Balloons were formed with an outer diameter of 0.119 in., a DWT of0.0015 in., and were subjected to 40 Mrads of radiation and demonstratedhigher burst pressures. For example, the balloon formed from the tubinghad a mean burst pressure of 285 psi (19.4 atm). Tubing not subjected toirradiation was formed into a balloon with an outer diameter of 0.1195in., a DWT of 0.00145 in., and a mean burst pressure of 252 psi (17.1atm).

EXAMPLES 14-15

In Examples 14 and 15, a polymer blend containing 90 weight % PETTraytuf 9506C manufactured by Shell, and 10 weight percent of anionomeric resin of ethylene and methacrylic acid, available under thetradename "SURLYN," manufactured by DuPont, were blended. The materialswere separately dried. Balloon tubing having an inner diameter of 0.021inches and an outer diameter of 0.0325 inches was extruded using this90/10 blend. The barrel and die temperatures of the extruder were setwith Zone 1 at 460° F., Zone 2 at 485° F., Zone 3 at 500° F., die 1 at520° F., die 2 at 520° F.

In Example 14, a balloon was formed and material had a mean burstpressure of 207 psi (14.1 atm).

In Example 15, tubing was formed as in Example 13. The tubing wassubjected to 20 Mrads of radiation. The balloons formed had a mean burstpressure of 255 psi (17.3 atm).

It will be apparent from the foregoing that while particular forms ofthe invention have been illustrated and described, various modificationscan be made without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

What is claimed is:
 1. A radiation cross-linked polymeric blend for usein making a catheter component consisting essentially of:about 60-77% byweight of the total blend composition of a polyester first polymericcomponent, said polyester being prepared from the group of dicarboxylicacids selected from aromatic dicarboxylic acids having from 8 to 14carbon atoms and aliphatic dicarboxylic acids having from 2 to 12 carbonatoms, and at least one glycol selected from the group consisting ofglycols having the formula HO(CH₂)_(n) OH, where n is an integer from 2to 10, neopentyl glycol and cyclohexane dimethanol; about 23-40% byweight of the total blend composition of a second polymer componenthaving a Shore hardness less than 75 D, selected from the groupconsisting of polyolefins having a density less than 0.93, ethylenecopolymers having the formula E'X' or E'X'Y', where E' is ethylene, andis 60-75% by weight of the ethylene copolymer, and where X' is 25-40% byweight of the ethylene copolymer, and X' is selected from the groupconsisting of methylacrylate, ethylacrylate, propylacrylate,butylacrylate, and mixtures thereof, and Y' is selected from the groupconsisting of α, β-ethylenically unsaturated monocarboxylic acids, α,β-ethylenically unsaturated dicarboxylic acids, and anhydridescomprising about 0.5-15% by weight of the ethylene copolymer, andpolyester block copolymers; and from about 0.25% to about 2.5% by weightof the total blend composition of a compatibilizing ethylene copolymerhaving the formula E/X/Y where E is ethylene, X is an α, β-ethylenicallyunsaturated monomer derived from at least one of alkylacrylate,alkylmethacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide,or mixtures thereof, where the alkyl groups contain 1-12 carbon atoms,and Y is an α, β-ethylenically unsaturated monomer containing a reactivegroup that forms a covalent bond with said first polymeric component andthat blends compatibly with said second polymer component; and whereinsaid polymeric blend is irradiated to provide said polymeric blend witha compliance of about 0.02-0.03 mm/atm as measured in terms of expansionper pressure applied to a catheter component formed from said polymericblend at a mean burst pressure of about 20 atm.
 2. The polymeric blendof claim 1, wherein said first polymeric component is selected from thegroup consisting of polyethylene-terephthalate,polybutylene-terephthalate, glycol modified polyethylene-terephthalate,1,4-cyclohexylene dimethylene terephthalate/isophthalate copolymer,linear homopolymer esters derived from aromatic dicarboxylic acids andglycols of the general formula HO(CH₂)_(n) OH where n is an integer from2 to
 10. 3. The polymeric blend of claim 1, wherein said first polymericcomponent is a polyester with glycol segments selected from the groupconsisting of ethylene glycol; 1,3-trimethylene glycol;1,4-tetramethylene glycol; 1,6-hexamethylene glycol; 1,8-octamethyleneglycol; 1,10-decamethylene glycol; 2,2-dimethyl-1,3-propane diol;1,3-propylene glycol; 1,4-butylene glycol; neopentyl glycol andcyclohexane dimethanol.
 4. The polymeric blend of claim 1, wherein X isselected from the group consisting of vinyl acetate, methylacrylate,butylacrylate, and methyl vinyl ether.
 5. The polymeric blend of claim1, wherein Y is an α, β-ethylenically unsaturated monomer containing areactive group selected from the group consisting of epoxide, maleicanhydride, isocyanate, or oxazoline.
 6. The polymeric blend of claim 1,wherein X is a moiety derived from at least one of alkyl acrylate, alkylmethacrylate, alkyl vinyl ether, carbon monoxide, sulfur dioxide, ormixtures thereof.
 7. The polymeric blend of claim 1, wherein Y isselected from the group consisting of glycidyl methacrylate, glycidylacrylate, maleic anhydride, and isocyanato-ethylmethacrylate.
 8. Thepolymeric blend of claim 1, wherein X is a moiety derived from at leastone alkyl acrylate, alkyl methacrylate, or mixtures thereof, where thealkyl groups contain 1-8 carbon atoms.
 9. The polymeric blend of claim1, wherein Y is selected from the group consisting of glycidyl acrylate,glycidyl methacrylate, and epoxide containing copolymerizable monomers.10. The polymeric blend of claim 1, wherein said polymeric blend isirradiated using ionizing radiation generated by any of an electronbeam, gamma rays, ultraviolet light, or a molecular beam.
 11. Thepolymeric blend of claim 1, wherein said polymeric blend is irradiatedby an electron beam in the range of about 10-100 Mrads.